The present invention relates generally to an illumination source for signs utilizing miniature fluorescent lamps. More particularly, the present invention is directed towards an illumination source for edge lit display signs, such as edge-lit emergency exit signs.
An illuminated display sign generally comprises a light source to illuminate a display surface upon which words, symbols, or other indicia are imprinted. Illuminated display signs include a variety of advertising signs, household number display signs, information bearing signs, and a variety of emergency information signs.
One common type of display sign in an emergency exit sign. Emergency exit signs include several different light source configurations. Exit signs are almost universally required in various types of commercial establishments under modem building codes, which specify the size, shape, and required luminance of the sign. FIG. 1 is a perspective view of an exit sign 100 in which the light source is configured to illuminate a display panel 130. The configuration shown in FIG. 1 is commonly known as an xe2x80x9cedge litxe2x80x9d emergency exit sign 100 because light generated in a housing 120 is coupled to an xe2x80x9cedgexe2x80x9d (entrance surface) 112 of a transparent display panel 110. Display panel 110 is shaped to form a light guide which couples light to an outer display surface 130. Display panel 110 is typically made from a plastic material with colored indicia. The plastic display panel 110 acts as a light pipe or optical guide that transmits light to painted or printed opaque or translucent indicia within panel 110. Light passing through and around the indicia illuminates the indicia, thus creating a contrast between the clear plastic and the colored indicia.
FIG. 2 is an exploded side view of prior art edge lit emergency exit sign 100. As can be seen in FIG. 2, a lamp 150 occupies most of the volume of housing 120. Lamp 150 is commonly a T-5 fluorescent lamp, which is a tube-shaped lamp with a diameter of at least about 16 millimeters. As shown in FIG. 2, commonly the diameter, D, of lamp 150 is greater than the width 170 of the plastic or glass panel sections 160, 162 comprising light guide 110. Depending upon the specific design geometry, typically less than 20-30% of the light emitted from lamp 150 enters guide 110 in a conventional emergency exit sign 100.
While FIGS. 1 and 2 show an emergency exit sign with only one display surface 130, it will be understood that edge lit emergency exit signs commonly have two opposed display surfaces such that two T-5 lamps 150 are placed side-by-side to illuminate two opposed side-by-side optical guides 110. The shape of optical guide 110 also has several different common shapes. Optical guide 110 may comprise planar or wedge-shaped pieces of glass or plastic. Thus while FIGS. 1-2 illustrate one common style of edge-lit emergency exit sign 100, it will be understood that there are several different commonly used styles of edge-lit emergency exit sign in use today.
Conventional edge-lit emergency exit signs have several drawbacks. One drawback is that an edge-lit emergency exit sign 100 has a substantial operating cost, consisting of electricity charges, replacement parts and related labor. Two T-5 lamps consume about 24 watts of input power. For many situations the exit sign must be illuminated at all times. The energy costs will depend upon local utility rates but can be significant in applications, such as office complexes, which have a large number of emergency exit signs. There are also significant maintenance costs. The lamps have a limited lifetime and must be frequently replaced. An edge lit sign with T-5 lamps typically has a useful lamp lifetime of about 12,000 hours. Since emergency exit signs are typically operated 24 hours a day, seven days a week, this corresponds to a useful lifetime of about 1.4 years. Conventional T-5 lamps are also hot cathode lamps which require the use of standard fluorescent lamp sockets to hold the lamps in place. In the confined space of an emergency exit sign the heat of the T-5 lamps tends to make the sockets brittle. This can necessitate replacement of the sockets as often as every three years, further increasing the maintenance costs.
Another drawback with using T-5 lamps to illuminate an edge lit sign is that it is difficult, given space constraints, to include a large enough battery in housing 120 to illuminate exit sign 100 during extended power outages. In addition to lamp 150, the sign must include other equipment such as a step down transformer, ballast, lamp sockets and holder, and a mounting mechanism to permit the lamp and socket holders to be inserted and removed from housing 120. There is not much room left over for an economical large capacity battery. Conventional edge lit emergency exit signs typically have a battery with sufficient energy for about 90 minutes of power to illuminate one T-5 lamp 150. While this is sufficient to address present statutory regulations, there is a growing interest in emergency exit signs which have sufficient battery power to provide two-to-four hours or more of backup power when normal line power is unavailable.
Light emitting diode (LED) light sources are one alternative to the use of T-5 fluorescent lamps in edge lit emergency exit signs. LED illumination sources are energy efficient and have a longer operating lifetime compared to T-5 lamps. Additionally, LED illumination sources typically can be powered from AC line voltage using a comparatively compact AC-DC power converter. FIG. 3 is an exploded perspective view of a prior art emergency exit sign 300 using an LED light source 330 including a plurality of LEDs 368. Exit sign 300 is similar to one sold commercially by LITHONIA LIGHTING(trademark) of Decatur, Ga. LED light source 330 is shaped to slide into a housing 352 and typically includes an electrical connector 362 to receive line power and an AC-DC voltage converter (not shown in FIG. 3) to convert AC line voltage into low-voltage DC suitable for driving the LEDs. Top and bottom surfaces 382, 384 of LED light source 330 are shaped to fit into slots 380 in housing 352. LED light source 330 typically includes about 60 LEDs for a dual faced sign in order to achieve a reasonable total light output. A diffuser panel 364 is disposed to diffuse the light from LEDs 368 prior to the light entering acrylic panels 354. Panels 354 are shaped to form two tapered optical guides with graphic symbols 356 spelling out the word xe2x80x9cEXIT.xe2x80x9d One advantage of LED light source 330 is that LEDs have a long operating lifetime, resulting in a cost savings over T-5 fluorescent lamps. Additionally, an LED light source 330 typically uses two-to-three watts of power for an exit sign with two opposed display surfaces, resulting in about a factor of eight-to-twelve energy saving compared with two T-5 lamps 150.
However, LED light source 330 has several drawbacks. One drawback is that the brightness of an edge lit sign 300 using LED light source 330 is typically only about ⅓ that of an edge lit sign 100 using two T-5 lamps 150. The low brightness of an LED light source 330 is a significant disadvantage because it reduces the distance at which individuals can see edge lit sign 300, particularly in large, darkened, or smoke-filled rooms. Another drawback is that LED sources tend to have less contrast than conventional white light sources. In exit signs illuminated by a conventional T-5 lamp, the panels are illuminated by a white light. The indicia, which are colored, convert the white light into colored light (e.g., red). There is a large contrast between the brightly light colored indicia and neighboring portions of the display surface, which are faintly lit by white light. Commonly available, low cost LEDs, however, are typically monochromatic, i.e., they produce light of a single color, such as red or green. Although the price and availability of high-powered LEDs at a variety of wavelengths (colors) is improving, a low cost embodiment of LED light source 330 will typically be limited to red LEDs or green LEDs. One consequence of a monochromatic LED light source 330 of a single color (e.g., red light) is that the contrast in the sign is reduced because the plastic display panels 354, in the regions between indicia, tend to faintly emit the light of the same color as the indicia and the corresponding monochromatic LED color. For example, if only red LED""s are used as a light source (with red colored indicia) the letters of the word xe2x80x9cEXITxe2x80x9d appear as bright red but on a faintly red background. The contrast is thus reduced compared with T-5 lamps and other white light sources. Another problem with a monochromatic LED light source 330 is that it cannot be used to make a universal retrofit kit, i.e., a kit to replace a conventional T-5 lamp in a pre-existing sign. The colored indicia of the display panels of pre-existing emergency exit signs typically come in several different colors, with red and green being the most common display colors. An LED light source with red LED is unsuitable for illuminating green colored display surfaces whereas green LEDs are unsuitable for illuminating red colored display surfaces.
Although emergency exit signs 100, 300 are one of the most common forms of edge lit display signs, there are also a variety of other types of edge-lit signs or displays. These include a variety of advertising and display signs in which light from a fluorescent lamp is channeled along a light guide to one or more display surfaces. In these applications, the monochromatic (single color) output of LED light source 330 may be a severe limitation. For example, many edge-lit advertising displays utilize multicolor graphical display surfaces which are inconsistent with a monochromatic light source 330.
What is desired is a new illumination apparatus for illuminating edge lit signs and displays which has a white light with a brightness comparable to conventional fluorescent lamps but which has a significantly lower power consumption, and longer life.
The present invention comprises an optical module to facilitate the use of miniature fluorescent lamps in edge-lit display signs and other lighting applications. The present invention is generally directed towards the problems of improving the coupling of light from the lamps to the display surfaces and to protecting the miniature fluorescent lamps from deleterious mechanical stresses, all self-contained in one compact module.
Broadly speaking, the optical module of the present invention is intended for use with a miniature tube-shaped fluorescent lamp having first and second flexible electrical leads attached to first and second ends of the lamp and comprises: an optical chassis having a first support surface and a second support surface; a first resilient socket having a receptacle shaped to receive the first end of the lamp; a first clamp coupled to said optical chassis, the first clamp shaped to engage the outer surface of the first socket; a second resilient socket having a receptacle shaped to receive the second end of the lamp; a second clamp coupled to the optical chassis, the second clamp shaped to engage the outer surface of the second socket; an optical reflector disposed on the first surface of said optical chassis; wherein the sockets are configured to resiliently support the lamp above the surface of the optical reflector in the assembled optical module with the leads of the lamp extending through the sockets. A ballast is preferably included in the optical module. The ballast preferably includes a voltage converter, such as an AC-AC voltage converter to convert AC line voltage into a voltage suitable for the lamp and/or a DC-AC voltage converter to convert a low voltage DC source, such as a battery, into a voltage suitable for the lamp.
In a preferred embodiment, the reflector is shaped to increase the amount of light coupled to an edge lit display sign. The shape of the reflector determines the angle at which reflected light rays impinge upon the entrance surface of the optical guide of an edge lit display. The reflector is preferably shaped to adjust the angle at which reflected rays enter the optical guide to improve the coupling efficiency.
One object of the present invention is an optical module that is self-contained and compact enough to contain lamps and all related components into one package which fits into the same space as only the T-5 lamps fit into. In a preferred embodiment, the width of the optical module is less than or equal to two T-5 fluorescent lamps and its associated ballast, thereby permitting the optical module of the present invention to be substituted for a T-5 optical module in pre-existing lighting applications, such as edge-lit emergency exit signs.
Another object of the present invention is an optical module which reduces the deleterious affects of mechanical shock and vibration on miniature lamps. In a preferred embodiment, the lamps are supported by resilient sockets with the lamps raised above the surface of the reflector by a distance of several millimeters, which permits the lamps to flex without striking the surface of the reflector in response to a mechanical impulse to the optical module. Additionally, the optical module preferably has surfaces which form a guard to protect the lamps from being struck thereby facilitating the transportation, insertion, and removal of the assembled module.
Still yet another object of the present invention is an optical module which is inexpensive to manufacture. In a preferred embodiment, the framework and support elements of the optical module are injected molded plastic pieces which snap together using a minimum number of screws or other metallic connectors.
Yet still another object of the present invention is an optical module for use with an ultraviolet lamp for use with fluorescent pigment display indicia.
A further object of the present invention is a universal light source for all display sign colors.
Yet further an object of the present invention is an optical module with a long operating lifetime.
Still yet further an object of the present invention is an optical module with a high efficiency and corresponding reduction in operating costs.